1. Field of the Invention
This invention relates to a cleaning device for removing a developer and dust adhering to a surface to be cleaned in an image forming apparatus. More particularly, the invention relates to a cleaning device which is made compact by shortening the length from the held portion of a cleaning member to the portion of the cleaning member which bears against the surface to be cleaned and in which the cleaning member can bear against the surface to be cleaned with a good contact pressure force. The image forming apparatus may be an electrophotographic copying apparatus, a micro instrument, a recording apparatus or the like. The surface to be cleaned may be the surface of a member to which a developer adheres, such as an image bearing member such as a photosensitive drum or a magnetic drum or a fixing roller.
2. Description of the Prior Art
FIGS. 1 and 2 of the accompanying drawings show examples of the cleaning device according to the prior art. Both of the cleaning devices of FIGS. 1 and 2 are for removing toner from the surface of the photosensitive medium of an electrophotographic copying apparatus by the use of a blade.
In the example shown in FIG. 1, a rectangular elastic blade 2 bears against a photosensitive medium 1a along the direction of movement thereof (the direction of arrow a). In this case, the combined drag R of a vertical drag N which the blade 2 receives from the photosensitive medium 1a and the friction force F between the photosensitive medium 1a and the blade 2 acts in a direction to pull the blade 2 away from the photosensitive medium 1a. Therefore, the force which blocks toner is weak and very often, toner particles collect beneath the blade and when toner particles collect at one location, they tend to readily extend over the full length of the blade, and this has often led to the necessity of removing the blade and cleaning the tip end edge portion thereof.
For this reason, in the example shown in FIG. 2, a rectangular elastic blade 2 is caused to bear against a photosensitive medium 1a in opposed relationship with the direction of movement thereof (the direction of arrow b). In this example, cleaning is effected at the obtuse angle side whereat the blade 2 intersects the photosensitive medium 1a. Thus, part of the combined drag R is stored as the elastic strain of the blade and all the remainder of the combined drag R acts as an effective cleaning force, and the blade 2 is pushed into the wedge-shaped space between a holder 3 and the photosensitive medium 1a, i.e., in the direction of the friction force F, so that the toner blocking capability is remarkably greater than in the example of FIG. 1 and accordingly, toner particles hardly collect beneath the blade and can be removed sufficiently. If, in this manner, the blade 2 bears against the photosensitive medium 1a in opposed relationship with the direction of movement thereof, the cleaning performance will be enhanced. However, the direction of the friction force F is the direction in which the blade 2 is reversed. Thus, to prevent such reversal phenomenon, the blade 2 must have a thickness greater than a predetermined thickness or a free length greater than a predetermined free length, and this has formed an obstacle in making the cleaning device compact. That is, an attempt to shorten the free length of the blade would result in an increased contact pressure force of the blade relative to the photosensitive medium, which in turn would lead to the increased danger of the photosensitive medium being damaged. As a countermeasure for this, it would occur to mind to decrease the thickness of the elastic blade, but in such case, the holding force in the held portion of the blade would not be dispersed uniformly and the deformation of the blade would become great during application of a pressure, and this has led to the possibility of the cleaning performance being reduced. That is, the free end of the blade 2 relative to the holder 3 is on a line P and, where the thickness of the blade 2 is constant, the stress of displacement of the blade 2 concentrates on points Q.sub.1 and Q.sub.2 and the blade 2 is liable to be displaced from these portions and thus, reversal of the blade is also liable to occur in these portions.